The investigations will focus on a hemic neoplastic condition of the marine mussel, Mytilus edulis, as a model for certain aspects of tumorigenesis in higher animals. Similar neoplastic conditions occur in a variety of bivalve molluscs on a world-wide basis. Previous studies have addressed certain aspects of the biology of these conditions, but questions regarding etiology, tumor development, molecular basis of neoplastic transformation, transmissibility, and effects of the neoplasia on host immunocompetence are still largely unanswered. Five areas will be investigated in this study: 1) determination of age and seasonal development of the condition by histological study of a known high prevalence field population of mussels; 2) isolate and characterize potential proto-oncogenes expressed in the mussel hemic neoplasia using molecular oncogene probes and determine chromosomal complement of cells at different stages in the development of the neoplasia in vivo by flow cytometric analysis; 3) test immunocompetence of affected animals in comparison with normal animals by challenge with an opportunistic pathogen and test, in vitro, the function of neoplastic hemocytes, as compared to normal cells by assays for cytoxicity and phagocytosis; 4) optimize selected and limited parameters for the in ivtro maintenance of the neoplastic cells for the purpose of enabling further studies in neoplastic cell transformation and cell function; and 5) investigate intra and interspecific transmissibility of the neoplasia by animal contact, whole cell, and cell-free filtrate inoculation and by inoculation of DNA extracted from neoplastic cells.